LANDSCAPING & EXTERNAL WORKS 71
SuDS design principles for a compliant, climate resilient solution
Michael McIvor-New at Tobermore explains how Sustainable Drainage System (SuDS) schemes are a viable and cost-effective way to achieve climate resilience and biodiversity net gain on both modern housing schemes and commercial projects.
A
ccording to the 2023 State of Nature report, 86% of habitats in the UK are not in good condition, and one in six species is at risk of extinction. To ensure new projects don’t further damage our fragile ecosystems, Biodiversity Net Gain (BNG) is now mandatory in England under Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act 2021). All projects (barring exemptions) must deliver a BNG of 10%, providing more and/or a better quality natural habitat than before construction started. This must be maintained for a minimum of 30 years. As well as driving habitat loss, climate change has altered the British weather. Winter rainfall is now 16% higher than it was between 1960 and 1990, and rainfall on the stormiest days increased by approximately 20%. At the same time, the desire for clean lines and practicality has led to the use of hard surfaces in many urban environments. Rainwater cannot be absorbed onsite, leading traditional drainage systems to quickly become overwhelmed, exacerbating fl ash and surface fl ooding. In England and Scotland, the National Planning Policy Framework states that SuDS must be used on developments with 10 dwellings or more (or the non-residential equivalent), unless it is inappropriate. Although Schedule 3 remains unlikely to come into force in England, Lead Local Flood Authorities (LLFAs) are pushing SuDS through as part of planning requirements. This does, however, vary between the different authorities. For example, Westminster, Haringey and Essex, amongst others, incorporate SuDS as a requirement
ADF JULY/AUGUST 2026
for planning approval. Meanwhile, over in Wales, Schedule 3 has been adopted, making SuDS a mandatory design component on all schemes. The legislation is backed by 22 SuDS Approval Bodies (SAB), which ensure projects meet national standards.
Legislative compliance with SuDS When designing SuDS, it’s best practice to ensure that the fi rst fi ve millimetres of rain, essentially normal rainfall, never leaves the site. On a well-designed SuDS scheme, 40% of the water volume can be accommodated by soil alone. For effective, compliant SuDS schemes, there are four design principles that should be followed: • Managing quantity of rainwater runoff; • Managing water quality and preventing pollution;
• Create amenities for people; • Improve biodiversity.
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The need to comply with both environmental legislation and ensure projects are climate resilient means that it is essential that architects rethink drainage and landscape design
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